[libc-commits] [libc] [libc][docs] Update docs to reflect new headergen (PR #102381)

[via libc-commits]

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@@ -8,27 +8,97 @@ Full Host Build
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    :local:
 
+.. note:: 
+   Fullbuild requires running headergen, which is a python program that depends on
+   pyyaml. The minimum versions are listed on the :ref:`header_generation`
+   page, as well as additional information.
+
 In this document, we will present a recipe to build the full libc for the host.
 When we say *build the libc for the host*, the goal is to build the libc for
-the same system on which the libc is being built. Also, we will take this
-opportunity to demonstrate how one can set up a *sysroot* (see the documentation
+the same system on which the libc is being built. First, we will explain how to
+build for developing LLVM-libc, then we will explain how to build LLVM-libc as
+part of a complete toolchain.
+
+Configure the build for development
+===================================
+
+
+Below is the list of commands for a simple recipe to build LLVM-libc for
+development. In this we've set the Ninja generator, set the build type to
+"Debug", and enabled the Scudo allocator. This build also enables generating the
+documentation and verbose cmake logging, which are useful development features.
+
+.. note::
+   if your build fails with an error saying the compiler can't find
+   ``<asm/unistd.h>`` or similar then you're probably missing the symlink from
+   ``/usr/include/asm`` to ``/usr/include/<HOST TRIPLE>/asm``. Installing the
+   ``gcc-multilib`` package creates this symlink, or you can do it manually with
+   this command:
+   ``sudo ln -s /usr/include/<HOST TRIPLE>/asm /usr/include/asm``
+   (your host triple will probably be similar to ``x86_64-linux-gnu``)
+
+.. code-block:: sh
+
+   $> cd llvm-project  # The llvm-project checkout
+   $> mkdir build
+   $> cd build
+   $> cmake ../runtimes \
+      -G Ninja \
+      -DCMAKE_C_COMPILER=clang \
+      -DCMAKE_CXX_COMPILER=clang++ \
+      -DLLVM_ENABLE_RUNTIMES="libc;compiler-rt" \
+      -DLLVM_LIBC_FULL_BUILD=ON \
+      -DCMAKE_BUILD_TYPE=Debug \
+      -DLLVM_LIBC_INCLUDE_SCUDO=ON \
+      -DCOMPILER_RT_BUILD_SCUDO_STANDALONE_WITH_LLVM_LIBC=ON \
+      -DCOMPILER_RT_BUILD_GWP_ASAN=OFF                       \
+      -DCOMPILER_RT_SCUDO_STANDALONE_BUILD_SHARED=OFF        \
+      -DCMAKE_EXPORT_COMPILE_COMMANDS=ON \
+      -DLLVM_ENABLE_SPHINX=ON -DLIBC_INCLUDE_DOCS=ON \
+      -DLIBC_CMAKE_VERBOSE_LOGGING=ON
+
+Build and test
+==============
+
+After configuring the build with the above ``cmake`` command, one can build test
+libc with the following command:
+
+.. code-block:: sh
+
+   $> ninja libc check-libc
----------------
lntue wrote:

right now in full build `libm.a` is built separately with `ninja libm`.  You might want to add it here, until we combine their cmake targets for full build similar to overlay mode.

https://github.com/llvm/llvm-project/pull/102381